>>> On 03.02.14 at 17:58, Roger Pau Monné<roger....@citrix.com> wrote:
> On 29/01/14 09:52, Jan Beulich wrote:
>>>>> On 28.01.14 at 18:43, Roger Pau Monne <roger....@citrix.com> wrote:
>>> + free_req(blkif, pending_req);
>>> + /*
>>> + * Make sure the request is freed before releasing blkif,
>>> + * or there could be a race between free_req and the
>>> + * cleanup done in xen_blkif_free during shutdown.
>>> + *
>>> + * NB: The fact that we might try to wake up pending_free_wq
>>> + * before drain_complete (in case there's a drain going on)
>>> + * it's not a problem with our current implementation
>>> + * because we can assure there's no thread waiting on
>>> + * pending_free_wq if there's a drain going on, but it has
>>> + * to be taken into account if the current model is changed.
>>> + */
>>> + xen_blkif_put(blkif);
>>> + if (atomic_read(&blkif->refcnt) <= 2) {
>>> + if (atomic_read(&blkif->drain))
>>> + complete(&blkif->drain_complete);
>>> }
>>> - free_req(pending_req->blkif, pending_req);
>>> }
>>> }
>>
>> The put is still too early imo - you're explicitly accessing field in the
>> structure immediately afterwards. This may not be an issue at
>> present, but I think it's at least a latent one.
>>
>> Apart from that, the two if()s would - at least to me - be more
>> clear if combined into one.
>
> In order to get rid of the race I had to introduce yet another atomic_t
> in xen_blkif struct, which is something I don't really like, but I
> could not see any other way to solve this. If that's fine I will resend
> the series, here is the reworked patch:
Mind explaining why you can't simply move the xen_blkif_put()
down between the if() and the free_ref().
Jan
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